The present invention relates generally to methods and instruments for measuring the concentration of a chromophore such as hemoglobin in tissue.
Spectrophotometric instruments and methods for measuring the amount of a tissue chromophore having a certain functional state (e.g., the percentage of oxidized hemoglobin or StO2, and the percentage of oxidized cytochrome aa3) are generally known and disclosed, for example, in the Anderson et al. U.S. Pat. No. 5,879,294, which is hereby incorporated by reference in its entirety. The Anderson et al. patent discloses in particular a measurement algorithm which makes use of scaled second derivative spectrum values.
The Kuestner U.S. Pat. No. 5,377,674 discloses a spectrophotometric instrument and method for measuring the total concentration of a chromophore such as hemoglobin in tissue. The measurement algorithm uses a single term ratio of second derivative absorbance measured at a wavelength at which hemoglobin absorption occurs (analyte wavelength), and a second derivative absorbance measured in a wavelength region where no hemoglobin absorption occurs (reference wavelength) (e.g, 2nd derivative of absorbance at 1740 nm / 2nd derivative of absorbance at 1346 nm).
There remains, however, a continuing need for improved instruments and methods for measuring the total concentration of chromophores such as hemoglobin in tissue.